The present invention relates to heat exchangers, which are mounted external to a section of flue pipe or are an integral part of a section of flue pipe.
Heat exchangers are known, which direct water in a pipe through a flue.
U.S. Pat. No. 4,122,801 of Burns describes a heat exchanger which first encircles water pipes in 2 circular rings around an exhaust flue, but then directs the water into coils within the exhaust flue. The external rings appear to be for positioning the water flow headers equally around the flue, not to preheat the water.
U.S. Pat. No. 4,211,187 of Farris discloses an energy conservation system for heaters that uses a heat exchanger in a furnace chamber or duct.
U.S. Pat. No. 4,136,731 of DeBoer discloses a heat transfer apparatus for supplementing a building heating and cooling system, using a heat exchanger in a furnace flue. DeBoer suggests an external heat exchanger, but provides no enabling details thereof.
Japanese patent no. JA0031286 of Satou discloses a heat transfer pipe for high temperature gases. It has a shell with multiple, non-axial connected heat exchangers.
U.S. Pat. No. 6,068,047 of Buchhave describes a heat exchanger for a sludge containment structure made of two rigid half shells, wherein sludge flows in the annular space enclosed by the shell halves and an inner sleeve in a spiral path external the spiral tubing with heating fluid flowing therethrough.
U.S. Pat. No. 4,484,564 of Erickson disclose a water heater utilizing exhaust gases from furnaces or stoves, but the recovery is through a coil inside an exhaust flue.
U.S. Pat. No. 1,990,056 of Van Daam describes passing water through a spherical corrugated chamber.
U.S. Pat. No. 4,251,028 of Nicolai discloses a preheater with an internal wall parallel to an external side wall with a water tight seal with pressure restraining capability. It does not disclose a coil of hollow heat conductive tubing enclosed within a substantially dry cavity.
U.S. Pat. No. 3,896,992 of Borovina and U.S. Pat. No. 2,521,462 of Kinzelmann both disclose water heaters that pass water through a spiral coil within an exhaust flue.
Canadian patent no. CA1271380 of Hampden describes a heat exchanger for air, not fluids, which is heated in a replaceable flue section. Hampden uses a blower to draw air through fins in an annular space.
U.S. Pat. No. 4,037,567 of Torres proposes an exhaust flue over the water heater having a spiral coil for heating water therein.
U.S. Pat. No. 4,120,267 of Wood describe a tube and plate heat exchanger with water heating coils inside a chamber, such as a gas heat duct or flue.
German patent no. DE 3340281A of Grabietz describes a flue within a jacket wherein coiled water tubes wrap around the inner flue pipe. However, the space between the tubes positioned over the inner flue and within the outer jacket are filled with solid, cast molten metal, instead of fibrous insulation.
Soviet Union patent no. SU0779719 of Ukrorgtekhstroi discloses a heat exchanger with inner fins, not coils, which has heat resistant end caps enclosing a flue pipe. The fins are spiraled, but they are not hollow and do not carry fluid therein. Ukrorgtekhstroi does not contain tubing wrapped around a flue pipe.
Furthermore, U.S. Pat. No. 4,401,261 of Brown also discloses directing water coils inside of flues.
It is therefore an object of the present invention to provide a heater exchanger for domestic hot water with ease of installation, maintenance and removal.
It is another object of the invention to provide a heat exchanger that is conveniently attached to an existing flue.
It is a further object of the present invention to preheat a domestic hot water supply.
It is yet another object of the present invention to boost return water temperature in a hydronic heating installation prior to reentry to a furnace coil.
It is still another object of the present invention to reduce fuel use and to reduce pollution and wear of the furnace and burner.
It is yet another object of the present invention to improve over the disadvantages of the prior art.
In keeping with these objects and others, which may become apparent, the present invention includes heat exchangers mounted external to a section of flue pipe or as an integral part of a section of flue pipe. The heat exchanger preheats the domestic hot water supply and boosts the return water temperature in a hydronic heating installation prior to reentry to the furnace coil. The heat exchanger reduces fuel use and reduces pollution and wear of the furnace and burner.
In a preferred embodiment, a split heat exchanger formed from two half shells forms a heat exchanger with conduits having flow reversals to enhance heat transference.
A typical heat exchanger installation includes an oil or gas burner located on a furnace or boiler having a flue pipe leading to a gaseous outlet, such as a masonry chimney. A short vertical flue section leads to a draft-regulating damper. The flue heat exchanger may be a coil of copper tubing wrapped around the flue section, which picks up heat from the heated flue gasses. The cold water source is coupled to a short length of convoluted flexible tubing with coupling flanges thereby allowing water to travel to and from the flue mounted heat exchanger.
In another embodiment two flue heat exchangers communicate with cold water entering the horizontal heat exchanger which is wrapped around a flue section having a mixture of hot flue gasses and some make-up ambient air from the draft regulating damper. This heat exchanger is plumbed in series with another heat exchanger wrapped around the vertical section of flue pipe below a damper. The second heat exchanger again increases the water temperature prior to entering the furnace hot water coil.
In another embodiment a heat exchanger is prefabricated as a standard flue section and substitutes for a length of flue. This heat exchanger has a central flue pipe section with heat exchanger tubing wrapped around its periphery. A tubular shell encases the tubing with openings allowing for both the water inlet and water outlet coupling flanges. A highly conductive conformable material fills the empty spaces within the shell to increase heat transfer.
In another embodiment, a hydronic heating system is a hydronic loop circulated by circulator pump forcing water into heating coil inside a boiler or furnace. In this system, it first flows through heat exchanger where it picks up waste heat from the flue.
In a further preferred embodiment a preformed heat exchanger coil is wrapped around a cylindrically shaped sheet larger in diameter than a section of flue. This sheet is not totally enclosed, but it has a small gap along its length.
In yet another embodiment, two coiled heat exchanger conduits are interleaved together around a flue pipe.
Each embodiment of the heat exchanger may include a safety pressure relief valve through which preheated water may exit.
Often when two or more different types of metals contact each other, the metals deteriorate, corrode or weaken at the point of contact. Therefore, each embodiment of flue heat exchanger may also be constructed such that both the metal tubing and the section of flue piping that the metal tubing is wrapped around are made from the same type of metal, preferably copper. In addition, each embodiment that contains this variation may also include gaskets located at each end of this flue section (preferably copper), such that the gaskets prevent direct contact between this flue pipe section and the flue pipe section made from a different type of metal.
In a further embodiment of this invention, the heat exchanger comprises of two identical sections, each essentially of the shape of a half cylindrical tube, with an internal diameter which matches the external diameter of a flue pipe. By just assembling the two halves around an existing flue pipe in-situ and bolting them together through flanges, it is unnecessary to disconnect flue pipe sections with the attendant debris usually encountered. Thus this embodiment is easier to install, lower cost (since the original flue pipe is retained), easier to package, and adaptable to single or split use, such as domestic hot water and hydronic heating.